Exploring the binding interaction of potent anticancer drug topotecan with human serum albumin: spectroscopic, calorimetric and fibrillation study

Exploring the interaction of a potent anti-cancer drug Selumetinib with bovine serum albumin: Spectral and computational attributes

The binding of drugs to plasma proteins determines its fate within the physiological system, hence profound understanding of its interaction within the bloodstream is important to understand its pharmacodynamics and pharmacokinetics and thereby its therapeutic potential. In this regard, our work delineates the mechanism of interaction of Selumetinib (SEL), a potent anti-cancer drug showing excellent effect against multiple solid tumors, with plasma protein bovine serum albumin (BSA), using methods such as absorption, steady-state fluorescence, time-resolved, fluorescence resonance energy transfer, Fourier transform infrared spectra (FTIR), circular dichroism (CD), synchronous and 3D-fluorescence, salt fluorescence, molecular docking and molecular dynamic simulations. The BSA fluorescence intensity was quenched with increasing concentration of SEL which indicates interactions of SEL with BSA. Stern-Volmer quenching analysis and lifetime studies indicate the involvement of dynamic quenching. However, some contributions from the static quenching mechanism could not be ruled out unambiguously. The association constant was found to be 5.34 × 105 M-1 and it has a single binding site. The Förster distance (r) indicated probable energy transmission between the BSA and SEL. The positive entropy changes and enthalpy change indicate that the main interacting forces are hydrophobic forces, also evidenced by the results of molecular modeling studies. Conformation change in protein framework was revealed from FTIR, synchronous and 3D fluorescence and CD studies. Competitive binding experiments as well as docking studies suggest that SEL attaches itself to site I (subdomain IIA) of BSA where warfarin binds. Molecular dynamic simulations indicate the stability of the SEL-BSA complex. The association energy between BSA and SEL is affected in the presence of different metals differently.

PROTEIN BINDING CHARACTERISTICS OF YOHIMBINE, A NATURAL INDOLE ALKALOID BASED DRUG FOR ERECTILE DYSFUNCTION

Even to this day, talking about sexual-dysfunctions largely remains a taboo. Hence less studies were recorded and fewer remedies given. Erectile dysfunction (ED) is one of the most commonly treated psychological disorders which leads to major distress, interpersonal limitation and reduces the quality of life & marriage. This study aimed to assess a plant-derived molecule, Yohimbine (Yoh, a β-carboline indole-alkaloid; often used for ED treatment) and its potential binding phenomenon with hemoglobin (Hb). Successful binding of the Yoh with Hb is evident from spectroscopic and molecular-docking results. Yoh quenched the fluorescence of Hb efficiently through static mode. The binding affinity was in the order of 10⁵ M^-1 with 1:1 stoichiometry. Thermodynamic analyses concluded that the protein-ligand association to be spontaneous and attributed by entropy-driven exothermic-binding. Non-polyelectrolytic factor was the core, dominating factor. The structural aspects have been deciphered through infra-red spectroscopy and computational-methods. The giant 3D-protein moiety was significantly perturbed through drug-binding. Hydrophobic forces and hydrogen bonding participation were stipulated by molecular modeling data. This study reveals the detailed interaction pattern and molecular mechanism of Hb-Yoh binding; correlating the structure-function relationship for the first time; therefore, holds enormous importance from the standpoint of rational and efficient drug-designing & development.

Electrochemical determination of epirubicin in the presence of topotecan as essential anti-cancer compounds using paste electrode amplified with Pt/SWCNT nanocomposite and a deep eutectic solvent

Epirubicin (EP) and topotecan (TP) are two major anti-cancer compounds for the treatment of breast cancer with serious side effects. Hence herein, a carbon paste electrode (CPE) amplified with Pt/SWCNT nanocomposite and a deep eutectic solvent (CPE/DES/Pt-SWCNT) were proposed as an analytical tool for the monitoring of EP in the presence of TP in the real samples. Amplification of sensor was improve EP oxidation signal about 2.73 times. Under the optimized conditions, EP determined by using differential pulse voltammetry (DPV) technique with linear dynamic range of 0.001-500 μM with limit of detection (LOD) of 0.8 nM. The CPE/DES/Pt-SWCNT offered influential ability for monitoring of EP in injection and dextrose saline samples with a recovery range of 97.4%-104.9%.

Probing the Role of Cu(II) Ions on Protein Aggregation Using Two Model Proteins

Copper is an essential trace element for human biology where its metal dyshomeostasis accounts for an increased level of serum copper, which accelerates protein aggregation. Protein aggregation is a notable feature for many neurodegenerative disorders. Herein, we report an experimental study using two model proteins, bovine serum albumin (BSA) and human serum albumin (HSA), to elucidate the mechanistic pathway by which serum albumins get converted from a fully folded globular protein to a fibril and an amorphous aggregate upon interaction with copper. Steady-state fluorescence, time-resolved fluorescence studies, and Raman spectroscopy were used to monitor the unfolding of serum albumin with increasing copper concentrations. Steady-state fluorescence studies have revealed that the fluorescence quenching of BSA/HSA by Cu(II) has occurred through a static quenching mechanism, and we have evaluated both the quenching constants individually. The binding constants of BSA-Cu(II) and HSA-Cu(II) were found to be 2.42 × 104 and 0.05 × 104 M-1, respectively. Further nanoscale morphological changes of BSA mediated by oligomers to fibril and HSA to amorphous aggregate formation were studied using atomic force microscopy. This aggregation process correlates with the Stern-Volmer plots in the absence of discernible lag phase. Raman spectroscopy results obtained are in good agreement with the increase in antiparallel β-sheet structures formed during the aggregation of BSA in the presence of Cu(II) ions. However, an increase in α-helical fractions is observed for the amorphous aggregate formed from HSA.

Synthesis, characterization, DNA binding, topoisomerase inhibition, and apoptosis induction studies of a novel cobalt(III) complex with a thiosemicarbazone ligand

In this study, 9-anthraldehyde-N(4)-methylthiosemicarbazone (MeATSC) 1 and [Co(phen)2(O2CO)]Cl·6H2O 2 (where phen = 1,10-phenanthroline) were synthesized. [Co(phen)2(O2CO)]Cl·6H2O 2 was used to produce anhydrous [Co(phen)2(H2O)2](NO3)33. Subsequently, anhydrous [Co(phen)2(H2O)2](NO3)33 was reacted with MeATSC 1 to produce [Co(phen)2(MeATSC)](NO3)3·1.5H2O·C2H5OH 4. The ligand, MeATSC 1 and all complexes were characterized by elemental analysis, FT IR, UV-visible, and multinuclear NMR (1H, 13C, and 59Co) spectroscopy, along with HRMS, and conductivity measurements, where appropriate. Interactions of MeATSC 1 and complex 4 with calf thymus DNA (ctDNA) were investigated by carrying out UV-visible spectrophotometric studies. UV-visible spectrophotometric studies revealed weak interactions between ctDNA and the analytes, MeATSC 1 and complex 4 (Kb = 8.1 × 105 and 1.6 × 104 M-1, respectively). Topoisomerase inhibition assays and cleavage studies proved that complex 4 was an efficient catalytic inhibitor of human topoisomerases I and IIα. Based upon the results obtained from the 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS) assay on 4T1-luc metastatic mammary breast cancer cells (IC50 = 34.4 ± 5.2 μM when compared to IC50 = 13.75 ± 1.08 μM for the control, cisplatin), further investigations into the molecular events initiated by exposure to complex 4 were investigated. Studies have shown that complex 4 activated both the apoptotic and autophagic signaling pathways in addition to causing dissipation of the mitochondrial membrane potential (ΔΨm). Furthermore, activation of cysteine-aspartic proteases3 (caspase 3) in a time- and concentration-dependent manner coupled with the ΔΨm, studies implicated the intrinsic apoptotic pathway as the major regulator of cell death mechanism.

Topoisomerase inhibition and albumin interaction studies of acridine-thiosemicarbazone derivatives

In the present study, acridine-thiosemicarbazones (ATD) derivatives were tested for their interaction properties with BSA through UV-Vis absorption and fluorescence spectroscopic studies. Both hyperchromic and hypochromic effects, as well as red or blue shifts were demonstrated after the derivatives were added to the BSA. Values for the binding constant (K_b) ranged from 1.62 × 10⁴ to 8.71 × 10⁵ M^-1 and quenching constant (K_SV) from 3.46 × 10² to 7.83 × 10³ M^-1 indicating a good affinity to BSA protein. Complementary, two compounds were selected to assess their inhibition activity against topoisomerase IIα enzyme, of which derivative 3a presented the best result. Moreover, to evaluate protein-ligand interactions, as well as the antitopoisomerase potential of these compounds, tests of molecular modeling were performed between all compounds using the albumin and Topoisomerase IIα/DNA complex. Finally, in silico studies showed that all derivatives used in this research displayed good oral bioavailability potential.

The interaction between human serum albumin and antidiabetic agent - exenatide: determination of the mechanism binding and effect on the protein conformation by fluorescence and circular dichroism techniques - Part I

The interactions between transport proteins and drugs are very important from the pharmacological point of view. In this study, using fluorescence and circular dichroism (CD) techniques, we investigated the interaction between human serum albumin (HSA) and incretin antidiabetic drug - exenatide. Moreover, the effect of common metal ions (Ca²⁺, Zn²⁺, Cr³⁺) on the exenatide-HSA binding - was also described. Based on the experimental data under pseudophysiological conditions, the calculated binding constant values are on the order of 10⁴ M^-1, and the constants are lower in the presence of metal ions. We observed the increase of the hydrophobicity near the tryptophan-214 residue in subdomain IIA, but almost no change in the hydrophobicity surrounding tyrosine residues. A similar effect on the tryptophan microenvironment is influenced by metal ions. The calculated thermodynamic parameters indicated that the characteristic electrostatic and hydrophobic interactions play an important role in the albumin-exenatide complexes. The CD studies showed that exenatide does not change the secondary structure of the protein but used metal ions have some impact on albumin α-helical content.Communicated by Ramaswamy H. Sarma.

Groove binding between ferulic acid and calf thymus DNA: spectroscopic methodology combined with chemometrics and molecular docking studies

Ferulic acid (FA), a dietary phenolic acid compound, is proved to possess numerous biological activities. Hence, this study was devoted to explore the interaction between FA and calf thymus DNA (ctDNA) by UV - vis absorption, fluorescence, circular dichroism (CD) spectroscopy combined with multivariate curve resolution-alternating least-squares (MCR - ALS) and molecular docking studies. The concentration curves and the pure spectra of compositions (FA, ctDNA and FA - ctDNA complex) were obtained by MCR - ALS approach to verify and monitor the interaction of FA with ctDNA. The groove binding mode between FA and ctDNA was confirmed by the results of melting analysis, viscosity measurements, single-stranded DNA experiments, and competitive studies. The binding constant of FA - ctDNA complex was 4.87 × 10⁴ L mol^-1 at 298 K. The values of enthalpy (ΔH°) and entropy (ΔS°) changes in the interaction were -16.24 kJ mol^-1 and 35.02 J mol^-1 K^-1, respectively, indicating that the main binding forces were hydrogen bonds and hydrophobic interactions. The result of CD spectra suggested that a decrease in right-handed helicity of ctDNA was induced by FA and the DNA conformational transition from the B-form to the A-form. The results of docking indicated that FA binding with ctDNA in the minor groove. These findings may be conducive to understand the interaction mechanism of FA with ctDNA and the pharmacological effects of FA. Communicated by Ramaswamy H. Sarma[Formula: see text].

Forskolin-loaded human serum albumin nanoparticles and its biological importance

In this study, forskolin-loaded human serum albumin nanoparticles (FR-HSANPs) were successfully prepared by incorporation and affinity-binding methods. FR-HSANPs were characterized by transmission electron microscope that most of them are circular in shape and size is around 340 nm. The drug loading was more than 88% and further sustained release profiles were observed as it is 77.5% in 24 h time. Additionally, the cytotoxicity results with HepG2 cells indicated that FR-HSANPs showed significantly higher cytotoxicity and lower cell viability as compared to free forskolin (FR). Furthermore, to understand the binding mechanism of human serum albumin (HSA) with forskolin resulted from fluorescence quenching as a static mechanism and the binding constant is 6.26 ± 0.1 × 10⁴ M^-1, indicating a strong binding affinity. Further, association and dissociation kinetics of forskolin-HSA was calculated from surface plasmon resonance spectroscopy and the binding constant found to be K_forskolin = 3.4 ± 0.24 × 10⁴ M^-1 and also fast dissociation was observed. Further, we used circular dichroism and molecular dynamics simulations to elucidate the possible structural changes including local conformational changes and rigidity of the residues of both HSA and HSA-forskolin complexes.Communicated by Ramaswamy H. Sarma.

The computational and experimental studies on a 1, 2, 3-triazole compound and its special binding to three kinds of blood proteins

A newly synthesized compound, ethyl 5-phenyl-2-(p-tolyl)-2H-1, 2, 3-triazole-4-carboxylate (EPPC) may be considered as a drug candidate and was exploited to study the structural and spectral properties by using quantum chemical calculation and multiple spectroscopic techniques. The results on theoretical spectrum of EPPC were consistent with experimental spectrum in great degree. In addition, EPPC has been as a special probe and investigated on the interactions with three kinds of blood proteins including human serum albumin (HSA), human immunoglobulin (HIgG) and bovine hemoglobin (BHb) by using UV-Vis, fluorescence spectroscopy and molecular modeling, respectively. Changes in various fluorescence and UV-Vis spectra were observed upon ligand binding along with a remarkable degree of fluorescence enhancement on complex formation under physiological condition with binding constant about 10⁵ order of magnitudes, which caused the variations of conformation and microenvironment of these proteins in aqueous solution. The obtained results from the thermodynamic parameters calculated according to the van't Hoff equation indicated that the entropy change ΔS° and enthalpy change ΔH° were found to be 0.168 KJ/mol K and 22.154 KJ/mol for EPPC-HSA system, 0.284 KJ/mol K and 54.408 KJ/mol for EPPC-HIgG system, and 0.228 KJ/mol K and 37.548 KJ/mol for EPPC-BHb system, respectively, which demonstrated that the primary binding pattern is determined by hydrophobic interaction. The results of docking and molecular dynamics simulation using three proteins crystal models revealed that EPPC could bind to three proteins well into hydrophobic cavity, which showed good consistence with the spectroscopic measurements.Communicated by Ramaswamy H. Sarma.

Multispectral and molecular docking investigations on the interaction of primethamine/trimethoprim with BSA/HSA

Primethamine (PMA) and trimethoprim (TMP) were investigated as traditional coccidiostats on the binding of bovine serum albumin (BSA) and human serum albumin (HSA) by multispectral and molecular docking techniques. The Stern-Volmer plots and time-resolved fluorescence measurement declared that PMA/TMP quenching the intrinsic fluorescence of BSA/HSA was static quenching process. The binding constants (K_a) and binding sites (n) were calculated at different temperatures. Meanwhile, thermodynamic parameters showed electrostatic forces played a leading role in the interaction of PMA/TMP with BSA/HSA. Some metal ions such as K⁺, Mg²⁺, Cu²⁺, Ca²⁺, Zn²⁺ and Fe³⁺ had no effects on the binding system. The UV-vis absorption spectra confirmed that the interaction between PMA/TMP and BSA/HSA did happen. The analyses of synchronous fluorescence, FT-IR and circular dichroism spectra illustrated that PMA/TMP changed the secondary structures of BSA/HSA. According to Förster non-radiative energy transfer theory, the binding distance between PMA/TMP and BSA/HSA was calculated. The binding location of PMA/TMP to BSA/HSA was identified as sub-domain IIA, which was further confirmed by molecular docking.Communicated by Ramaswamy H. Sarma.